Conventionally, an interlayer insulating film is formed for insulation between interconnection layers in a multilayer interconnection structure on a semiconductor substrate or the like.
In such a multilayer interconnection structure, a problem of signal delay due to the parasitic capacitance between interconnections and the interconnection resistance has become unignorable and it has been required to use an interlayer insulating film having a low permittivity (Low-k).
As such an interlayer insulating film, attention has been paid to the fact that a fluorocarbon film (hereinafter referred to as a CFx film) has a very low permittivity and thus can reduce the parasitic capacitance between interconnections. However, the CFx film is very weak against water and poor in adhesion. Therefore, the CF film is formed on an underlayer such as an SiCN layer, an Si3N4 layer, or an SiO2 layer, but there has been a problem in the bottom and top surfaces of the CF film (i.e. the beginning and end of the film formation).
Conventionally, a CFx film is formed by the use of a plasma processing apparatus using a fluorocarbon gas (referred to as a CFx gas, e.g. a C5F8 gas), for example, as described in Patent Document 1.
As described in Patent Document 2, this CFx gas is originally used for etching and thus there has been a problem that if the plasma treatment temperature is high, an underlayer is etched to produce a silicon fluoride (SiF4) gas.
Further, there has been a problem that water and gases such as CFx and SiF4 are released from the surface of the formed CF film to form a contamination source.
Patent Document 3 describes that a formed CFx film is annealed in an N2 atmosphere at 400° C. to 450° C., so that outgassing after the film formation is small in amount.
Further, plasma treatment is performed using a single rare gas when forming an oxide film, a nitride film, an oxynitride film, or the like as an underlying metal on a silicon semiconductor. In the case of using a single rare gas, use is made of a krypton (Kr) gas or a xenon (Xe) gas having a large sectional area for collision with electrons and a low plasma electron temperature for the purpose of reducing plasma damage to post-treatment (e.g. see Patent Document 4).    Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 2002-220668    Patent Document 2: Japanese Unexamined Patent Application Publication (JP-A) No. 2002-16050    Patent Document 3: Japanese Unexamined Patent Application Publication (JP-A) No. H11-162962    Patent Document 4: Japanese Unexamined Patent Application Publication (JP-A) No. 2002-261091